Attempts have been made for many years to devise effective means inserted within an inflatable tire for permitting safe and extended driving in the event of blowout or other deflation of the tire. Such past efforts have been extensively discussed in my prior U.S. Pat. No. 3,635,273 dated Jan. 18, 1972 and the more recent reissue thereof, U.S. Pat. No. RE 28,196 dated Oct. 15, 1974, so this background need not be here repeated.
The structure of the tire insert disclosed and claimed in said prior patent and reissue thereof is unique in providing an inexpensive, easily mountable tire insert formed of a plurality of arcuate members which firmly and directly engage the wheel or rim in a manner to rotate with (i.e. as part of) the wheel or rim under normal conditions when driving on an inflated tire, but to slip circumferentially of the wheel or rim when the insert becomes load bearing by reason of deflation of the tire. The insert, in other words, functions as a roller in such load bearing operation with the outer surface of the insert rolling with little or no relative slippage along the inner surface of the tire tread and substantially all slippage necessary to account for the difference in circumference of the inner surface of the tire tread and the outer surface of the insert taking place between the inner surface of the insert and the wheel or rim. This type of slippage is facilitated by selection of appropriate materials, suitably plastics such as ultra high molecular weight (hereinafter referred to as UHMW) polyethelene or polypropylene, at the inner periphery of the insert. Composite structural materials have also been used.
Inserts of this structure have been extensively used and tested and have been shown to effectively prevent loss of control in the event of blowout at speeds of the order of 70 to 75 m.p.h. and to permit extended driving at moderate speeds without damage to the insert or further damage to the tire (beyond such damage as may have caused a sudden deflation). In the event of a slow leak, such as is sometimes encountered by parking too close to a curb, one may drive to a service station for replacement air and be assured that there has been no damage to the tire by reason of driving while the tire was deflated.
In most instances a motorist experiencing a flat tire will not be more than 10 or 15 miles from an appropriate service area for tire repair. If traveling 35 to 40 m.p.h., the motorist should not create any hazard even on a busy highway. The above mentioned tire inserts readily and repeatedly permit this type of operation. In fact, it has been found that sustained travel for about 20 miles at 35 m.p.h. is necessary before there is sufficient heat build up to interfere with the intended function of the tire insert. By including within the assemblage a small amount of water soluble lubricating fluid, such for example as a liquid nonionic surfactant, it is possible for the tire insert to meet the arbitrary and seemingly unrealistic objectives of the tire and auto industry of being capable of sustained run-flat driving for 50 miles at 50 m.p.h. with a one-inch cut in the sidewall causing zero internal air pressure.
Based on this type of performance in extensive testing, considerable interest in the above mentioned insert has been generated within the tire and automotive industries, but one limitation prevents automotive companies from adopting the improved tire insert as original equipment thereby eliminating the need for the extra tire and wheel now conventionally carried by every motorist. This problem is the substantial investment in equipment for automatically mounting inflatable tires on wheels or rims and the impossibility, with a structure which requires clamping the insert to the wheel or rim while the tire is half mounted thereon, of accomplishing this step during the automatic tire mounting operation. The production delays and labor costs for manual installation are not acceptable to a new car manufacturer.
While this problem in no way limits use of the insert on existing motor vehicles or the provision of such inserts as optional equipment to be installed at the point of delivery to the customer desiring such equipment, it will be apparent that there is a real need for making this safety feature acceptable and practical for inclusion as original equipment in the manufacture and assemblage of motor vehicles.